system-count forced in the middle of a movement?

Can anyone think of a way to (easily/automagically) force a desired
system-count within a certain section of a score, without resorting
to manual breaks?

For example, let's say in the middle of my string quartet I have a
fugal section (not a separate movement!) that I think fits nicely on
9 systems -- I would love to force Lilypond to set that section
according to the fixed system count, but use automatic spacing to
flow the rest of the movement (i.e., before and after the section in
question) around that 9-system chunk.